Tool support for object-oriented patterns

Abstract

A software (design) pattern describes a general solution for a recurring design problem. The solution is mostly described in terms of an abstract design structure expressed in design elements such as classes, methods and relationships (inheritance, associations).

This paper describes a prototype tool that supports working with design patterns when developing or maintaining object-oriented programs. The tool provides three integrated views on a program: the code (classes, methods, etc.), a design view (abstraction of the code plus additional information not in the code) and occurrences of design patterns in the program.

The tool assists developers using patterns in three ways:

• • Generating program elements (e.g. classes, hierarchies) for a new instance of a pattern, taken from an extensible collection of “template” patterns

• • Integrating pattern occurrences with the rest of the program by binding program elements to a role in a pattern (e.g. indicating that an existing class plays a particular role in a pattern instance)

• • Checking whether occurrences of patterns still meet the invariants governing the patterns and repairing the program in case of problems

Through the use of an existing refactoring package, the tool supports the use of patterns both in forward engineering and in backwards engineering, i.e. documenting occurrences of patterns in existing programs and modifying the program to better reflect the pattern's structure.

The tool is implemented in Smalltalk and has been applied to identify pattern occurrences in several non-trivial (Smalltalk) applications and to reorganize these subsequently.